We haven't heard too much from Trent@MyGeekShow since he restructured his time late last year. He has however just uploaded a video outlining some exciting news.
These new professionally-built 4S packs are based on Panasonic's NCR18650GA Lithium-Ion cells which offer comparable energy density but with upwards of twice the power density as Panasonic's well known NCR18650B.
With the primary factor prohibiting use of Panasonic's NCR18650Bs in a broader range of unmanned aerial craft having been the relatively conservative power density (compatible only with the most efficient craft) as well as the limited availability of suitably sized and terminated packs, this new offering is a fantastic option for many smaller fixed-wing (AXN/Bixler/Wicked Wing XL) and mini-multirotor (<350 ships, not fpv racing) flyers who are chasing a bit of extra endurance.
The only problem I can see at this point is that they appear to be available exclusively via Amazon and shipping is not available to me here in the land down under. It is a shame too because I would love to grab half a dozen or so for my park flyer!
Comments
To be clear, I'm not saying these things are snake-oil. They do have higher energy density. It's just not the 200% that some people claim based on the mAH/Kg measurement.
I think 18650's are great for airplanes, which only require maximum power on take-off, and then have much less current and voltage needs in cruise. And they can work on world-record-setting quadcopters with no payload hovering in a windless environment.
But I haven't been able to get them to work at all in a functional Copter scenario with high hover throttles. The slope of the voltage drop is just too great.
Rob_Lefebvre - I use 4S 5200mAh 10C Multistars in one of my quads and have found them to be great performers. I also use a bunch of the smaller 1400mAh 65C packs on my fpv mini, which have massive sag even at full charge (not an aggressive setup - 3S/2000KV/6x3).
Funny you should mention the importance of thinking in Watt-Hours - click on the NCR18650B hyperlink above (back to Trent's original "better than lipo" blog post) and read the second last comment in the thread (note - the points I was responding to have since been deleted). BTW - Panasonic provide gravometric energy density specifications for each chemistry - NCR18650B is 243Wh/kg, while NCR18650GA is 223Wh/kg. As you can see above, even at the 10-Amp rate the NCR18650GAs are still good for around 90% of what it says on the tin.
The discharge curves pictured above and which can be found in the linked datasheet from Panasonic tell you all you need to know about how much the voltage drops under load. Further test results can be found here. The discharge curves are indeed perhaps a bit steeper than one might expect from a 10C prismatic lipo under the same conditions (but these are not rated at 10C, so that is perhaps not at all surprising).
Trent - No worries mate. I reckon these are gonna be a go'er! The larger capacity packs with internal balancing sound hard, good luck with those!
Trent, I think you missed the point I'm trying to make. It is not whether or not a pack can put out X# of Watts. What I am interested in is the actual delivered Watt-Hours/KG of these cells. The area under the curve, if you will, as you measure discharge under an actual load.
Often 18650's are credited has having twice the density of LiPo, but my brief testing has showed only about 20% more than Multistar 10C LiPo batteries (which are really 5C).
I've done a project trying to get a VTOL vehicle flying with them, using 2500 mAH 18650's rated at 10C, and it can only fly about 5 minutes before the voltage output is so low that it can't hover anymore, having dropped below 3.5V. I recharge them and can only put back in 800 mAH.
I understand the batteries are being pushed too hard, although they are within the manufacturers (false) spec. I didn't design the system, was just trying to work with it. I put an 800mAH LiPo battery on it, and it flies for 7 minutes.
If you look at the discharge curve of many 18650's, they start at 4.2V, but quickly drop to 3.5V, and are not depleted until 2.5V. Compare this to a typical LiPo which starts at 4.2V, drops to 4.0-3.8V in bulk, and then is done by about 3.0-3.5V. Look at the area under the curve.
Thank you for sharing this Quadzimodo! As those who have flown NCR cells before, you know these are great alternatives to LiPos.
A few answers to questions:
1 - Currently only available on Amazon.com in USA, however, we're looking at getting it in other stores, especially outside the USA. If you have a store you'd like to buy these from, let them and me know!
2 - 3S and 6S versions are in the making. Also "flat" versions that could fit better in a flying wing. Also researching how to make 2P3S with only one 3S balance plug (will need internal circuitry). Lots to do!
3 - Charging these is the same as you would any other charger - just use a 4S LiPo setting at charge at 1.6A for maximum storage.
4 - Real world testing has been done (NCRB's were used on the USA trip!), but videos showing NCRGA are coming out asap! Still limited time to make videos (dang day job!) but coming soon (this month).
5 - Voltage drop is more pronounced due to higher internal resistance (aka lower C rating), hence 400W peak at 35A (11.4 volts). It still can put the 400W out however, which is insane for a pack that carries 50Wh and weighs 200g.
Thank you all for your interest and feedback. Keep the questions / ideas coming!
-Trent
@Damian Yes.
@Rob If you pull around 1C from these packs, you should ot see higher voltage drop.
I would love to see some real world test numbers for the actual Watt-Hours/KG of these cells, compared to a 10C LiPo pack like the Turnigy Multistars.
Everybody looks at mAH/KG, but we actually fly on Watt-Hours, not Amp-Hours.
I've done some cursory looks at the data, and find that due to 18650 cell's higher voltage drop under load, the actual W-H/Kg is not nearly as impressive as most people believe. But I don't have any of these cells to actually prove the point.
Could you use a normal $10 balanced LiPO charger for these Li-Ions?
Or do you need a special one?
@Tommy
There are using the cells which you have mentioned. Currently highest capacity 18650 batteries have 3500mah but it is highly probable to see a 3800mah version later this year or beginning of 2017.
Nice battery :)
But this cell is even better isn't it?
https://www.fasttech.com/products/1420/10010486/2399401
RM Aviation - Thanks mate. Yeah, I am familiar with these cells and actually purchased a spot welder for the purpose of building my own packs. As Trent points out, and you are no doubt aware yourself, putting these things together is not a simple proposition due to the tricky nature of the task and ease with which one can heat stress the cells without specialized equipment. The OEM finish on these packs is also pretty nice and the price very reasonable, so I expect they will make a convenient and attractive proposition for many.
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